Month: May 2018

Essay 15. The Trouble With Translocations: Does Snake Relocation Help or Hinder?

Python with Cat, Brown in Office.png
Two local snake species from Brisbane, QLD, Australia, both relocated by the author. ABOVE – A non-venomous Carpet Python (Morelia spilota) consuming an urban prey item, in this case a wandering neighbourhood cat. BELOW- A highly venomous Eastern Brown Snake (Pseudonaja textilis) in an office lunchroom, on the kitchen bench in between the toaster and kettle.

“I hate and fear snakes, because if you look into the eyes of any snake you will see that it knows all and more of the mystery of man’s fall, and that it feels all the contempt that the Devil felt when Adam was evicted from Eden.” – Rudyard Kipling, The Return Of Imray.

Kipling, evidently, disliked snakes. Like many of his era and before, perhaps less today (or so one hopes), snakes were seen not only as a dangerous, venomous, marauding villain, but also a portent of evil, the Devil’s own infiltrator lurking in the Garden, one who knows our weaknesses and tempts us into our sinful demise and exile. While certain cultures like Hinduism and Buddhism included powerful, even benevolent serpent gods (such as the Nagas, now the namesake of the Naja genus of cobras), snakes have an almost universally negative perception in western culture. Here in Australia, where some of the World’s most highly venomous snakes are regular backyard visitors, the attitudes are often no different (1). It’s common to hear “A good snake is a dead snake!”, and no small degree of urban legend when discussing these animals, such as the interbreeding of pythons and venomous Brown Snakes to form dangerous “hybrids”, despite these taxa being in separate families (Pythonidae and Elapidae), and therefore, in some senses, as likely as cats and dogs (Felidae and Canidae families respectively) to produce viable offspring (2).

Aside from the confusion of whether to call ensuing hybrid young a “Cog” or “Dat”, this hybrid-Brown Snake myth exemplifies some of the misunderstandings regarding snakes. They are a hugely persecuted but equally ecologically important clade, some adapting better than others to human modified environments (1,3). As such, many snake fanatics find themselves initially falling into and then following a passion for reptiles as a career in research, management, or herpetoculture. For some, such as myself, we wind up in a career involving snake relocation; the safe capture and removal of snakes causing a risk to people, pets, or in the case of rescues, themselves (4). Following a quick health assessment, we then aim to find suitable habitat within their own ecosystem for release, all working under local and federal wildlife and safety legislation.

While a far cry from the more traditional method of dispatch, usually involving some sort of weaponry, I certainly was rather quick to assume that my own actions have had a net positive effect on snake populations and local ecosystems. Here, at the outset of writing and researching this ramble, nearly five years into managing a snake removal service and even longer as a reptile keeper, carer, and general wildlife enthusiast, I still believe fauna translocation can be a useful method for people and ecosystems. But my conviction that what we do is always positive is certainly not as strong. A number of literature reviews on the subject (5, 6, 7) and a plethora of published studies cast further doubt on the suitability of translocation as a management tool. And so, while I am clearly ethically compromised and heavily biased, may I humbly suggest that we still can, and indeed should, discuss the ins and outs of snake translocation in brief, then move on to examine some pros and cons, based on what evidence is available.

In the case of snakes, translocations are often employed to mitigate threats involved in wildlife interactions, often in urban areas (4,8). In my own area of Brisbane, by far the majority of calls are for non-venomous carpet pythons. Looking at some of my own data (from the current financial year, spanning 1st of July 2017 to 18th of April 2018), the vast majority of captures are Carpet Pythons (Morelia spilota, N=181), followed by Common Tree Snakes (Dendrelaphis punctulata, N=22), followed closely by Eastern Brown Snakes (Pseudonaja textilis, N=21). After these comes an assortment of minor players; four Yellow-Faced Whip Snakes (Demansia psammophis), three Red-bellied Black Snakes (Pseudechis poriphyriacus), three Brown Tree Snakes (Boiga irregularis), and a few others, for a total of 38 venomous and 206 non-venomous snakes. These non-venomous species are only moved if there’s a genuine threat; if there are pets at risk on the property, if they’re indoors, or if they’re stuck somewhere people need access to (like cars, offices, or work sites). Handling is, ideally, done with an aim to minimise stress where possible and avoid unnecessary agitation.

Moving wildlife is always a troublesome prospect. As ecosystem engineers on a massive scale, finding suitable human habitat is easy almost anywhere in the world. Most other species are locally adapted to their more immediate environments, but so are populations and individuals. While some species have a fantastic spatial memory which they require for movement within their home range (1, 9, 10), others are simply the local variants which survived best given their adaptive advantage, for example, perhaps dark animals living on dark backgrounds survive their first season while lighter variants are picked off by predators (6, 11). Out of any litter, it’s likely that only a few will pass through the selective sieve of time and chance to reach reproductive age, leaving rather well adapted local populations. In translocating animals, the local conditions are hardly likely to be exactly the same at the release site, thus certain local adaptations may no longer be appropriate, or could even become a detriment. The results tend to suggest that relocation, particularly long distances, is generally detrimental to the animal (5, 6, 7).

To what scale we’re interfering with locally adapted snakes is difficult to determine, however there are multiple studies at least attempting to assess the impact, often by radio-tracking translocated individuals. In the USA, relocated timber rattlesnakes (Crolatus horridus) were shown to have a mortality rate of 55% and more erratic daily movements averaging 123.8 meters per day, compared to 11% and 36.9 meters in resident snakes (12). Following translocation, Heiken et al. (13) also found elevated corticosterone and testosterone levels in Pacific Rattlesnakes (C. oreganus) suggesting the procedure can be rather stressful. Relocated Western Diamond-backed Rattlesnakes (C. atrox) also showed three times higher mortality rates then resident rattle snakes (14), and resident Eastern Hognose Snakes (Heterodon platirhinos) also survived three times longer than transplants (15).

Such findings aren’t restricted to reptiles in the United States. In India, King Cobra (Ophiophagus hannah) studies show significant increases in home range size and average daily movement following relocation (16). The white-lipped pit viper (Trimeresurus albolabris) is commonly found in homes and urban areas in South China where they’re relocated to national parks, with some surprising negative consequences (17). After a 3km translocation, individuals took long straight movements but not homing towards any capture point, although certainly exposing them to risks and increased mortality. Furthermore, translocation resulted in a failed, delayed, or extended onset of winter hibernation, a potentially significant mortality factor (18). Translocated female snakes did not reproduce the following season and suffered 80% mortalities, while all males died before the first summer (17).

Here in Australia, several species also show negative responses following translocation. Tiger Snakes (Notechis scutatus) in Victoria were shown to have home ranges six times the size of residents, and make longer movements than residents do (140 vs 64 meters) (19). A recent project by reptile ecologist Ashleigh Wolfe at Western Australia’s Curtin University (20) on Dugites (Pseudonaja affinis), a southwest Australian member of the brownsnake genus common around the city of Perth, showed a troubling result. All four Dugites were killed following relocations over 3km, while residents moved less than 200 meters also showed 50% mortality. Translocated Dugites also had greater activity ranges and travel distances, prior to death of course. It seems that while certain species like carpet pythons seem well suited for urban life (3, 21), larger, venomous species like the Dugite may struggle, perhaps more so when their movements are disturbed.

A range of unrelated taxa appear to show similar responses. Brush-Tailed Possums (Trichosurus vulpecula) in Melbourne, Australia, and White-Tailed Deer (Odocoileus virginianus) Illinois, USA, both also show high mortality rates, and translocation has frequently failed to limit human-wildlife conflicts in Saltwater Crocodiles (Crocodylus porosus), Grey Wolves (Canis lupus), and Brown Bears (Ursus arctos) to name just a few (5, 6, 7). While it’s fascinating reading, the Herculean pile of translocation studies in other species is going nowhere for now, and I fear I’m in danger of laboring the point. Back to snakes.

Translocation, it seems, is at best a temporary solution to an animal’s presence, not so much a measure against further interactions, nor is it ideal for the animal itself. What does all this mean for snake translocations here in Australia? There does, at the very least, appear to be ways to minimise the impact. Various study species, including Eastern Massassaugas (Sisturus catenatus, 18) in Canada, Western (C. oreganus, 22) & Timber Rattle Snakes in the US (C. horridus, 12, 23) through to Dugites in Western Australia (P. affinis), suggests a positive relationship between translocation distance and mortality rate. This makes intuitive sense, with shorter distance translocations less likely to move an animal out of suitable local habitat which it is adapted to, or even keeping an individual within its own home range (12, 22, 23).

Sadly, we must now return to the human-wildlife conflict. Studies have shown that even short distance translocation is hardly an ideal mitigation measure, as many animals, including Tiger snakes, may return to their homes in or near urban areas shortly after release (19, 7, 10). Here we come to an interesting point. I’d like to suggest that not all nuisance or threatening animals are equal. Let us quickly compare our humble Tiger snake from Victoria to a mammalian predator, for example, a Coyote (Canis latrans). No matter how hungry it is, the former does not, unless mistaken by an unfortunately sudden appearance of toes or pinky fingers in front of it’s face, see you as a prey item.

The same cannot be said of a hungry Coyote wandering through the suburbs (24). Here in Australia, our dangerous Elapid snakes generally make every possible effort to flee and avoid humans (1). Also, snakes are often small and have a habit of exploring crevices and caves, leading them to occasionally enter homes via open doors and windows. Moving them back outdoors or off the property, away from pets and people, is often all that’s needed as they’ll generally disappear into cover immediately after release. Moving large, highly intelligent and spatially sensitive predators that return home and see livestock or humans as prey, like bears, wolves or, closer to home, the saltwater crocodile (Crocodylus porosus), is much more challenging (5, 7, 25).

Another consideration is the specific ecology of the snake in question. For instance, while both displayed an increased risk, the mortality rates following translocation were much lower for Tiger snakes (N. scutatus) than for Dugites (P. affinis). In Butler et al. (2005)’s study, discussed earlier, 3 of 8 translocated and 2 of 6 resident tiger snakes died (19). While there are obviously other variables to consider, the aforementioned 100% mortality rate (4 from 4) following 3km translocation for Dugites is striking (20). Could something about this species be putting it at more risk following translocation? For comparison, consider the 1999 Timber Rattlesnake (Crolatus horridus) study (12), with many individuals surviving after being moved between 8 and 172km. Of two individuals moved 172km, creatively named FOX6-92 and FOX1-91, both survived two seasons of tracking, one eventually succumbing to disease, the other surviving the whole study period. I won’t say who survived, you’ll just have to read the paper, but their name started with FOX…moving on!

Different requirements of the species being moved, as well as the characteristics of surrounding habitat, should be considered. For example, generalist feeders might be more likely to find suitable prey in unfamiliar habitats than specialists (7). Perhaps the Tiger snake, a much more generalist predator, is more capable of finding any number of lizards, birds, rodents, frogs, or even carrion, while the Dugite struggles to find new grounds to hunt rodents and lizards (1, 20). Or perhaps, since these studies haven’t been replicated in different areas, the suburbs surrounding Perth where the Dugite study took place are more hostile to snakes in general than the wetland park where the Tiger snake study occurred. Impacts of attaching transmitters aside, a 50% mortality rate even for resident Dugites moved no more than 200 meters (3 out of 6 died) shows just how dangerous the urban landscapes can be for snakes (20). Previous work by Wolfe and Co. found that urban Dugites were in worse condition, generally smaller and less likely to have prey in their stomachs, suggesting the typical response for urban-adapted predators (i.e. exploiting novel food sources) is not the case for this species (26).

This brings up several questions. What exactly is it about Dugites that makes them so vulnerable? Is it something about their life history or something about Perth’s urban environment? If it’s a case of life history, for example being a specialist feeder, what other species share those characteristics and do they correlate in terms of translocation success? Or, if it’s something about Perth’s urban environment, perhaps an abundance of roaming cats, what other cities are suicide for snakes, and why? It might be interesting to examine how several sympatric snake species (#newbandname #SSSS), perhaps Eastern Brown Snakes (P. textilis) and Red-Bellied Black Snakes (Pseudechis poriphyriacus) fare around large, urban centers along the coast, such as Brisbane, Sydney, and Melbourne.

Nevertheless, until all these variables are known, like a snake catcher under a house, we must grope on in the darkness. However, as a snake catcher, I assume we can try to live by a few short rules based on what we know:

  1. Try not to move snakes. It’s counter-intuitive, but the best job is one where you’ve educated a frighted caller and not moved anything. You don’t get paid, but that’s life.

  2. If you must move an animal, minimize the distance and choose appropriate habitat, taking into account the species’ ecology, in particular, movement patterns and home ranges, if these are known.

Thus, what is appropriate must be decided on a species by species basis. This, again, gets complicated. For example, Eastern Brownsnakes have been shown to have a larger home range than Tiger snakes, as calculated by Minimum Convex Polygon (MCP, 5.8 vs 3.88 hectares), suggesting some Brownsnakes may handle more distant translocations (19, 27). Mortality rates in Dugites suggest otherwise (20). Further, MCPs can vary hugely. Tiger snakes from the New England plateau have much smaller MCPs of 0.77ha (albeit from small sample size, 2 snakes over 6 weeks, Shine, 1979), and MCPs of the large, highly mobile Burmese pythons in the USA Everglades can range between 170 to a massive 8,740 hectares (10, 28). Even within one Australian species, the carpet python (Morelia spilota), a variety of MCPs have been recorded; 17.6ha (21) and 22.5ha (29), while male and female Diamond Pythons (a dark, speckled M. spilota morph from the Sydney region) have MCPs of 52ha and 27ha respectively (30). Red-Bellied Black Snakes also display a wide range of MCPs, from 0.02ha to over 40ha between individuals, and larger in males during breeding season (9). MCPs and home ranges are thus probably better used as guides, and only relied upon if the spatial ecology of the species is well studied.

Unfortunately this is rarely the case. Rarely do we have a good understanding of a snake species’ movement ecology, though there are exceptions, and generalizations are certainly possible; invasive Burmese Pythons clearly move further than Carpet Pythons, which move further than Brown Snakes, which move further than Tiger Snakes. What movement ecology means for survivorship following translocation, I would suppose, depends on the distance to, extent of, and quality of the new habitat, as well as the condition of the animal before and after handling. Ideally, controlling for these factors, translocation can be improved upon, as appears to have been the case over the years with increasing success rates over the last few decades, likely due to improved methodology (6). While hardly ideal, an understanding of each species home range, their ecology, and the local ecosystems at capture and release seems, to me, the best way forward for now. Nonetheless, while it’s not a huge sample size, four from four dead Dugites (20) speaks for the need for more research, and to potential for our well meaning actions, when not examined, to cause more harm than good.

A final thought. What might be the outcome if we abandon snake translocation entirely? While individuals may certainly be at risk, would snake populations be any worse off if we left an educated general public to deal with snakes on their own, without the experience and training required of professional snake handlers? And what viable options other than translocation are available to us? I don’t know the answer to these questions, but it seems that we are, for now, continuing with the less-than-perfect tool of translocations for snake management. More research into its impacts on various species and local ecosystems certainly would not go awry. Let’s stay on our toes.

References:

  1. Shine, R (1991) Australian Snakes: A Natural History. Reed Books, Sydney, New South Wales.

  2. https://snakesonthebrainblog.wordpress.com/2017/02/19/essay-10-hybridization-and-the-myth-of-python-brownsnake-crossbreeding/

  3. Fearn, S., Robinson, B., Sambono, J., Shine R. (2001) Pythons in the pergola: the ecology of ‘nuisance’ carpet pythons (Morelia spilota) from suburban habitats in south-eastern Queensland. Wildlife Research. 28, 573–579

  4. Shine, R. & Koenig, J. (2001) Snakes in the garden: an analysis of reptiles ‘‘rescued’’ by community-based wildlife carers. Biological Conservation. 102, 271–283

  5. Fischer, J. & Lindenmayer, D.B. (2000) Review: An assessment of the published results of animal relocations. Biological Conservation. 96, 1-11

  6. Germano, J.M. & Bishop, P.J. (2008) Review: Suitability of Amphibians and Reptiles for Translocation. Conservation Biology. 23. 1, 7–15

  7. Massei, G., Quy, R.J., Gurney, J., Cowan, D.P. (2010) Can translocations be used to mitigate human–wildlife conflicts? Wildlife Research. 37, 428–439

  8. Welton, R.E., Liew, D., Braitberg, G. (2017 Incidence of fatal snake bite in Australia: A coronial based retrospective study. Toxicon 131, 11-15

  9. Shine, R. (1987) Intraspecific Variation in Thermoregulation, Movements and Habitat Use by Australian Blacksnakes, Pseudechis porphyriacus (Elapidae). Journal of Herpetology. 21. 3, 165-177

  10. Hart, K.M, Cherkiss, M.S., Smith, B.J., Mazzotti, F.J., Fujisaki, I., Snow, R.W. (2015) Home range, habitat use, and movement patterns of non-native Burmese pythons in Everglades National Park, Florida, USA. Animal Biotelemetry. 3:8

  11. Dubey, S., Zwahlen, V., Mebert, K., Monney, J., Golay, P., Ott, T., Durand, T., Thiery, G., Kaiser, L., Geser, S.N., Ursenbacher, S. (2016) Diversifying selection and color-biased dispersal in the asp viper. BMC Evolutionary Biology. 15,99

  12. Reinert, H.K. & Rupert, R.R. Jr. (1999) Impacts of Translocation on Behavior and Survival of Timber Rattlesnakes, Crotalus horridus. Journal of Herpetology. 33. 1, 45-61

  13. Heiken, K.H., Brusch, G.A., Gartland, S., Escallón, C., Moore, I.T., Taylor, E.N., (2016) Effects of long distance translocation on corticosterone and testosterone levels in male rattlesnakes. General and Comparative Endocrinology.

  14. Nowak, E.M., Hare, T., McNally, J. (2002) Management of ‘nuisance’vipers: Effects of translocation on western diamond-backed rattlesnakes (Crotalus atrox). Biology of the Vipers. Eagle Mountain Publishing: Eagle Mountain, UT, USA. 535–560.

  15. Plummer, M.V. & Mills, N.E. (2000). Spatial ecology and survivorship of resident and translocated hognose snakes (Heterodon platirhinos). J. Herpetol. 34, 565-575.

  16. Barve, S., Bhaisare, D., Giri, A. (2013)A preliminary study on translocation of “rescued” King Cobras (Ophiophagus hannah). Hamadryad. 36. 2, 80-86

  17. Devan-Song, A., Martello, P., Dudgeon, D., Crow, P., Ades, G., Karraker, N.E. (2016) Is long-distance translocation an effective mitigation tool for white-lipped pit vipers (Trimeresurus albolabris) in South China? Biological Conservation. 204, B, 149-468

  18. Harvey, D.S., Lentini, A.M., Cedar, K., Weatherhead, P.J. (2013) Moving massasaugas: insights into rattlesnake relocation using Sistrurus c. catenatus. Herpetol. Conserv. Biol. 9, 67–75.

  19. Butler, H., Malone, B., Clemann, N., (2005) Activity patterns and habitat preferences of translocated and resident tiger snakes (Notechis scutatus) in a suburban landscape. Wildlife Research. 32, 157–163.

  20. Wolfe, A., Fleming, P., Bateman, B. (2018) Impacts of translocation on a large urban-adapted venomous snake. Wildlife Research. (JUST ACCEPTED, 30 March 2018, WR17166)

  21. Shine, R. & Fitzgerald, M. (1996) Large snakes in a mosaic rural landscape: the ecology of carpet pythons Morelia spilota (Serpentes: Pythonidae) in coastal eastern Australia. Biological Conservation. 76, 113–22.

  22. Brown, J.R., Bishop, C.A., Brooks, R.J. (2009) Effectiveness of short-distance translocation and its effects on western rattlesnakes. J. Wildl. Manag. 73, 419–425.

  23. Sealy, J. (1997). Short-distance translocation of timber rattlesnakes in a North Carolina state park, a successful conservation and management program. Sonoran Herpetologist. 10, 94–99.

  24. Poessel, S.A., Gese, E.M., Young, J.K. (2017) Landscape and Urban Planning Research paper Environmental factors influencing the occurrence of coyotes and conflicts in urban areas. Landscape and Urban Planning. 157, 259-269

  25. Campbell, H.A., Dwyer, R.G., Irwin, T.R., Franklin, C.E. (2013) Home Range Utilisation and Long-Range Movement of Estuarine Crocodiles during the Breeding and Nesting Season. PLoS ONE. 8(5): e62127.

  26. Wolfe, A.K., Bateman, P.W., Fleming P.A. (2017) Does urbanization influence the diet of a large snake? Current Zoology. 39, 1-8.

  27. Whitaker, P.B. & Shine, R. (2003) A Radiotelemetric study of movements and shelter-site selection by free-ranging brownsnakes (Pseudonaja textilis, Elapidae). Herpetological Monographs. 17. 1, 130-144.

  28. Pittman, S.E., Hart, K.M., Cherkiss, M.S., Snow, R.W., Fujisaki, I., Smith, B.J. (2014) Homing of invasive Burmese pythons is South Florida: evidence for map and compass senses in snakes. Biol Lett. 10, 10, 20140040.

  29. Pearson, D., Shine, R., Williams, A. (2005) Spatial ecology of a threatened python (Morelia spilota imbricata) and the effects of anthropogenic habitat change. Austral Ecol. 30, 261–74

  30. Slip, D.J. & Shine, R. (1988) Habitat use, movements, and activity patterns of free-ranging diamond pythons, Morelia spilota spilota (Serpentes: Boidae): a radiotelemetric study. Aust Wildlife Res. 15, 515–31.